STEREO-A's reawakening
posted: July 29, 2015

As discussed in a previous news item (see 4 June 2014), both STEREO spacecraft are on the other side of the Sun as seen from Earth. This is called a superior solar conjunction - see diagram underneath for the position of both spacecraft. For some time, each spacecraft is blocked by the solar disk making it impossible to communicate with it or receive data or images from it. On top of that, being so close to the Sun, the radio signals are disturbed by the solar radio emission for quite some time before and after the conjunction.

For STEREO-A, the radio silence is finally over. Starting 8 July, the STEREO operations team gradually awakened STEREO-A from its hibernation using the powerful antennas from the Deep Space Network. Instruments and cameras were gradually turned back on. The first extreme ultra-violet and coronagraphic images became available on 11 July, and were put online over the next few days. STEREO-A's current location provides a view on which active regions are about to turn over the east limb as seen from Earth and thus will become visible to us. The imagery is also important to determine if any coronal mass ejections are earth-directed or not.

So it's good to have at least one of the twins back online. The situation for STEREO-B is more problematic. Indeed, STEREO-B is already offline since 01 October 2014 after contact with the spacecraft was lost following two simultaneous failures in the attitude control system (see STEREO status). Recovery efforts are currently planned for later this year. Hopefully they are successful such that the views of the entire solar surface, such as the map underneath, will remain available for a few more years. The situation can be followed up at STEREO's news site.